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WO2008007336A2 - Procédé de production de matériau à base de diamant - Google Patents

Procédé de production de matériau à base de diamant Download PDF

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Publication number
WO2008007336A2
WO2008007336A2 PCT/IB2007/052751 IB2007052751W WO2008007336A2 WO 2008007336 A2 WO2008007336 A2 WO 2008007336A2 IB 2007052751 W IB2007052751 W IB 2007052751W WO 2008007336 A2 WO2008007336 A2 WO 2008007336A2
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less
nitrogen
ppm
preferably greater
diamond
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WO2008007336A3 (fr
Inventor
Carlton Nigel Dodge
Francis Alizuli Tshisikhawe
Grant Charles Summerton
John Olaf Hansen
Keith Barry Guy
Louis Louwrens Naude
Robert Charles Burns
Simon Craig Lawson
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Element Six Technologies Pty Ltd
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Element Six Technologies Pty Ltd
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J3/00—Processes of utilising sub-atmospheric or super-atmospheric pressure to effect chemical or physical change of matter; Apparatus therefor
    • B01J3/06—Processes using ultra-high pressure, e.g. for the formation of diamonds; Apparatus therefor, e.g. moulds or dies
    • B01J3/062—Processes using ultra-high pressure, e.g. for the formation of diamonds; Apparatus therefor, e.g. moulds or dies characterised by the composition of the materials to be processed
    • C—CHEMISTRY; METALLURGY
    • C30—CRYSTAL GROWTH
    • C30B—SINGLE-CRYSTAL GROWTH; UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL; PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; APPARATUS THEREFOR
    • C30B29/00—Single crystals or homogeneous polycrystalline material with defined structure characterised by the material or by their shape
    • C30B29/02—Elements
    • C30B29/04—Diamond
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2203/00—Processes utilising sub- or super atmospheric pressure
    • B01J2203/06—High pressure synthesis
    • B01J2203/0605—Composition of the material to be processed
    • B01J2203/061—Graphite
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2203/00—Processes utilising sub- or super atmospheric pressure
    • B01J2203/06—High pressure synthesis
    • B01J2203/0605—Composition of the material to be processed
    • B01J2203/062—Diamond
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2203/00—Processes utilising sub- or super atmospheric pressure
    • B01J2203/06—High pressure synthesis
    • B01J2203/065—Composition of the material produced
    • B01J2203/0655—Diamond
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2203/00—Processes utilising sub- or super atmospheric pressure
    • B01J2203/06—High pressure synthesis
    • B01J2203/0675—Structural or physico-chemical features of the materials processed
    • B01J2203/068—Crystal growth

Definitions

  • This invention relates to a method for producing diamond material, in particular this invention relates to a method for producing diamond material of defined and useful form and to diamond material produced to have such predetermined qualities.
  • the present invention therefore relates to the growth or synthesis of large single crystals of diamond by either the temperature gradient method under high pressure high temperature (HPHT) conditions, or otherwise by the phase-balance or graphite conversion process where excess pressure is the motive force for growth.
  • HPHT high pressure high temperature
  • the diamond material in the finished product it is important for the diamond material in the finished product to have uniform optical properties. It is well known that the optical properties (for example optical absorption) of diamond may be strongly affected by its nitrogen content and that this is in turn sensitive to the crystallographic orientation (e.g. ⁇ 100 ⁇ or ⁇ 111 ⁇ ) of the growth surface of the diamond. This has suggested that synthesis of material with low nitrogen content is more suitable for applications of this type.
  • the morphology of HPHT synthesised diamond crystals can be tuned to a certain extent by varying the growth temperature.
  • a limit to the extent to which extremely cubic or octahedral crystals can be produced using temperature alone to tune the morphology There is therefore a need for a method to achieve crystals with these extremes of crystal morphology, preferably with sizes above particular thresholds and for some applications with uniform optical, electrical and mechanical properties as well.
  • CMI crystal morphology index'
  • Crystals which are bounded by a mixture of ⁇ 100 ⁇ and ⁇ 111 ⁇ type faces have CMI values that are greater than 0 and less than 8.
  • a graphical representation of the CMI index is given in Figure 1.
  • the seeds from which diamond crystals are grown are generally retained in a ceramic carrier.
  • the presence of the carrier means that crystals can generally only grow into half of the full solid angle. After growth the seed crystal remains exposed on the seed face of the grown large crystal.
  • the CMI is defined using the view of the crystal from the side furthest from the seed. (See Figure 2)
  • the present invention relates to a process for synthesising large diamond crystals of a defined and useful form, with low metallic impurity content and at a high rate of growth.
  • the crystal growing process is conducted at High Pressure and High Temperature (HPHT) using either the temperature gradient process or alternatively using the phase balance (graphite conversion) process and where materials to be used for the growth of the diamonds are augmented by a controlled quantity of one or more components or vectors that have the effect of introducing nitrogen into the growing diamonds in a controllable and reproducible way.
  • One such vector is a cobalt metal powder that has preferably been treated in ammonia at a temperature of not less than 700 0 C before combining with the other metal components used in the HPHT synthesis solvent catalyst.
  • a method of producing diamond material including the step of providing a reaction mass including sufficient nitrogen to result in diamond material having a nitrogen content of at least 100 ppm in combination with a transition metal vector and subjecting the reaction mass to a temperature of greater than 1200 0 C and a pressure greater than 5 GPa.
  • synthesised diamond material having at least two, preferably at least three, more preferably at least four of the following characteristics (i) to (v): (i) a nitrogen content of at least 100 ppm;
  • CMI crystal morphology index
  • the nitrogen concentration in the grown diamond is also affected by the growth temperature and the nitrogen concentration in growth environment.
  • the outcome is that diamond with a nitrogen concentration in a given range can be grown in forms that depend on the growth temperature in the way indicated in Table 1.
  • the morphology of the stones varies continuously from fully-cubic to fully octahedral and the boundaries between the temperature bands in Table 1 are consequently somewhat blurred.
  • Table 1 Combinations of morphology and nitrogen content achieved in different growth temperature ranges.
  • FIG. 3 A graphical representation of table 1 can be seen in Figure 3 where entries in the grid of Figure 3 match the corresponding entries in Table 1.
  • This invention relates to the growth or synthesis of large single crystals of diamond by the either the temperature gradient method under high pressure high temperature (HPHT) conditions, or otherwise by the phase-balance or graphite conversion process where excess pressure is the motive force for growth.
  • synthesised diamond material may be interchangeably referred to as diamond, diamond crystal, crystal, stone, diamond material and synthesised diamond material.
  • nitrogen contents generally greater than one part per million (1 ppm), and more generally greater than 50 ppm.
  • the nitrogen that enters the growing diamond is derived principally from the atmospheric air that is entrapped in the starting materials used for synthesis, and to a lesser extent it is derived from the small amount of nitrogen, typically less than 50 parts per million by mass, that is present as an impurity in the metals used as catalyst solvents.
  • Nitrogen is present because the catalyst metals and other materials were prepared in most cases using processes that are at least in part open to the earth's atmosphere, and that atmosphere contains a constant percentage of nitrogen of near to 80 percent by volume. Some of this nitrogen is inevitably dissolved or physically entrained in the metals giving low but finite nitrogen contents of typically a few tens of parts per million by mass.
  • N ⁇ ioo ⁇ > is greater than the nitrogen content in the octahedral sectors, N ⁇ in ⁇ (S. Satoh, H. Sumiya, K. Tsuji, S. Yazu, 'Science and Technology of New Diamond' Proc. 1st Int. Conf. on New Diamond Science and Technology, Tokyo, 24-26 Oct 1988, p351-355).
  • nitrogen content is used to denote the total content of nitrogen within the synthetic diamond. It is known to those skilled in the art that the nitrogen can be present in one of several forms in the diamond.
  • One such form is the single substitutional nitrogen atom, where a nitrogen atom replaces a carbon atom at a site in the diamond lattice.
  • Diamond in which this is the major form of nitrogen present, and where the nitrogen content is generally greater than one part per million (1 ppm) is classified as being 'Type Ib' (for a description of the diamond classification system, see Field, The Properties of Natural and Synthetic Diamond', Academic Press, London, 1992, p669).
  • Almost all diamond grown by the HPHT method, and in particular in the regimes of temperature and pressure normally applied for this method, is of type Ib. When the crystal has been subjected to subsequent processing at high temperatures and high pressures, the form of the nitrogen present in the crystal may become altered.
  • the present invention relates to diamond crystals containing high total concentrations of nitrogen, irrespective of the form of the nitrogen.
  • the concentration of nitrogen can be measured with accuracy using the techniques of FTIR absorption spectroscopy using the 1130 cm "1 feature in the infrared region of the absorption spectrum and an absorption coefficient-concentration relation of 22 ppm/cm "1 (G. S. Woods et al, Phil. Mag., B62 (1990), p589-595).
  • the concentration of nitrogen in aggregated forms (such as A- centres composed of nearest neighbour nitrogen atoms) can also be measured using FTIR absorption spectroscopy.
  • the total nitrogen concentration can be measured using techniques such as Secondary Ion Mass Spectroscopy (SIMS).
  • High concentration - stable nitrides such as F ⁇ 3 N contain tens of thousands of ppm of nitrogen and so only a small quantity of the dopant must be added and distributed rather well. This is difficult to achieve on a controllable and reproducible basis and so is unsuited to anything other than research.
  • the solvent catalyst contains either nickel or cobalt or nickel and cobalt as a major component.
  • the solvent catalyst contains at least one of the elements manganese, chromium and copper as an additive.
  • a major component in a solvent catalyst is present at a level of more than about 5% by weight.
  • An additive in a solvent catalyst is present at a level of less than about 1% by weight.
  • the nitrogen in the diamond so produced is increased from a level of 100 to 150 ppm in the case where no additive is used, to over 100 ppm, preferably greater than 150 ppm, preferably greater than 200 ppm, preferably greater than 250 ppm, preferably greater than 300 ppm, preferably greater than 350 ppm, preferably greater than 400 ppm, preferably greater than 450 ppm, preferably greater than 500 ppm, preferably greater than 550 ppm, preferably greater than 600 ppm, preferably greater than 650 ppm, preferably greater than 700 ppm, preferably greater than 750 ppm, preferably greater than 800 ppm, preferably greater than 850 ppm, preferably greater than 900 ppm, preferably greater than 950 ppm, preferably greater than 1000 ppm.
  • the shapes of the diamonds grown under these conditions is best described as a 'blocky shape', predominantly comprising of either ⁇ 100 ⁇ facets or ⁇ 111 ⁇ facets, with little or no minor facets such as ⁇ 110 ⁇ , ⁇ 113 ⁇ and ⁇ 115 ⁇ and little or no curvature of the facets and edges. 3.
  • the diamonds are strongly cubic in shape (i.e. exhibit predominantly ⁇ 100 ⁇ facets) and this shape favours the efficient production of plates, logs and prisms as might be important in technical applications.
  • this means the materials morphology can be described by having a CMI less than 5, preferably a CMI less than 4, preferably a CMI less than 3, preferably a CMI less than 2.
  • the crystals are strongly octahedral in shape (i.e. exhibit predominantly ⁇ 111 ⁇ facets) as might be useful when there is a requirement for this form. Such a requirement might be in the gem industry, where the octahedral shape is more usually seen in the natural diamond crystals most often used in that industry.
  • the material of this invention is found to have a low total transition metal concentration dissolved in the lattice.
  • the total transition metal content in the lattice is less than 100 ppm, preferably less than 80 ppm, preferably less than 60 ppm, preferably less than 50 ppm, preferably less than 40 ppm, preferably less than 30 ppm, preferably less than 20 ppm, preferably less than 10 ppm, preferably less than 5 ppm, preferably less than 2 ppm, preferably less than 1 ppm.
  • the total Ni concentration is less than 100 ppm, preferably less than 80 ppm, preferably less than 60 ppm, preferably less than 50 ppm, preferably less than 40 ppm, preferably less than 30 ppm, preferably less than 20 ppm, preferably less than 10 ppm, preferably less than 5 ppm, preferably less than 2 ppm, preferably less than 1 ppm.
  • the total Al concentration is less than 100 ppm, preferably less than 80 ppm, preferably less than 60 ppm, preferably less than 50 ppm, preferably less than 40 ppm, preferably less than 30 ppm, preferably less than 20 ppm, preferably less than 10 ppm, preferably less than 5 ppm, preferably less than 2 ppm, preferably less than 1 ppm.
  • the total Co concentration is less than 100 ppm, preferably less than 80 ppm, preferably less than 60 ppm, preferably less than 50 ppm, preferably less than 40 ppm, preferably less than 30 ppm, preferably less than 20 ppm, preferably less than 10 ppm, preferably less than 5 ppm, preferably less than 2 ppm, preferably less than 1 ppm.
  • the total Fe concentration is less than 100 ppm, preferably less than 80 ppm, preferably less than 60 ppm, preferably less than 50 ppm, preferably less than 40 ppm, preferably less than 30 ppm, preferably less than 20 ppm, preferably less than 10 ppm, preferably less than 5 ppm, preferably less than 2 ppm, preferably less than 1 ppm.
  • transition metal impurities can be quantified and characterized using techniques such as SIMS and photoluminescence. For example it is reported in the literature that under 325 nm excitation PL features thought to be associated with Co are observed at 523.8, 544.5, 561.7, 580.7 nm. With excitation at 632.8 nm further peaks at 657.7, 669.2, 720.8, 722.8, 793.2, 807.6, 863.9, 868.8, 882.6, 884.7 nm 887.4 and 992.3 nm are also thought to be associated with Co.
  • the carbon source material from which the diamond is grown could also be diamond. This includes diamond synthesized through this route. This provides an additional route to further enhance the nitrogen in the grown material by starting with a source material containing a high nitrogen concentration.
  • the diamond grown by the teachings of this invention as the vector for nitrogen (where the term 'vector' has the meaning of 'the means by which the nitrogen is transported from the synthesis environment into the growing diamond crystal') in a subsequent synthesis cycle when using the reconstitution, or temperature-difference method of diamond growth.
  • the diamond that is used as the vector for nitrogen is also the source of carbon for the growth of the large diamond crystals. This may not appear to be as attractive as the use of a metal or metal-alloy vector, in the application as an economical solution to an industrial problem.
  • the use of diamond as a source material may confer other advantages in the design of an HPHT synthesis process.
  • the vector for the addition of nitrogen to the crystal growth process could be diamond of high nitrogen content, whether grown by the teachings of this invention or produced in some other way.
  • the nitrogen content of diamond when grown by the HPHT method can be controlled to range from less than 1 ppm of nitrogen through the action of nitrogen getters and other techniques, through to levels of greater than 1000 ppm by adding additional nitrogen to the catalyst (Z. Z. Liang, X. Jia, H. A. Ma, C. Y. Zang, P. W. Zhu, Q. F. Guan, H. Kanda, Diamond Relat. Mater., 14 (2005), p1932).
  • the added nitrogen also promotes octahedral growth when the temperature of the synthesis process is in the high range of temperatures available for growth.
  • the range of temperatures that are available for growth will depend upon the pressure at which the growth occurs. Generally, a higher pressure allows for growth over a larger range of temperatures.
  • the inventors have studied diamond growth within two growth regimes, one capable of producing high CMI (near 8) crystals the other, low CMI (near 1).
  • the action of increasing the nitrogen content of the catalyst leads to increased nitrogen incorporation within the grown diamond as well as a higher CMI (i.e. more octahedral crystals).
  • the action of increasing the growth temperature had the effect of increasing the CMI, leading to more octahedral crystals, to a greater extent than could be achieved solely by adding nitrogen. This result is unexpected.
  • the inventors have found that when pursuing conditions for low CMI growth, a lower growth temperature was required, as has been disclosed in the prior art, but that here, surprisingly, addition of nitrogen increases the tendency towards lower CMI growth, the opposite to what was seen in the high CMI regime. In this case, the action of reducing the growth temperature favours the growth of crystals with a more cubic morphology, but at a reduced growth rate.
  • the nitrogen concentration within the central ⁇ 100 ⁇ sector that sector which grows in the direction of the carbon source material, has a tendency to decrease during the course of the growth cycle, whereas it remains more constant in the ⁇ 111 ⁇ sector.
  • the cause of this change is at present not known. It could be due to a loss of the added nitrogen from the HPHT growth cell, or to temperature or pressure changes. The temperature of the growing face will increase as it moves upward and towards the carbon source, because of the temperature gradient used to promote crystal growth, but we would not expect this temperature difference to be sufficient to result in such a distinct change in morphology.
  • Morphologies of the grown crystals were recorded from captured images using the CMI system as defined above. Selected samples were sectioned along ⁇ 110 ⁇ planes and polished on a diamond polisher's scaife. The sector structures were examined both optically and using a photoluminescence microscope such as the DTC Diamond ViewTM instrument. The distribution of nitrogen between sectors was determined from the polished plates by FTIR spectra using a Nicolet 750 Magna IR spectrometer with a 0.5 mm aperture. More detailed scans of the change in nitrogen within sectors were determined using a Nicolet Nic plan microscope through a 0.1 mm aperture. These measurements enable the change of morphology during growth to be related to the nitrogen incorporation between sectors.
  • the frequency distribution of nitrogen measurements taken by FTIR over a representative sample taken from the layer must be such that 90% of the measurements vary by less than 50%, and preferably by less than 30%, expressed as a percentage of the mean. In all later discussion this is what is defined as ⁇ N ('delta N').
  • a bulk measurement of the uniformity of the concentration of nitrogen in a parallel sided diamond sample can be made using FTIR absorption spectroscopy in the following way.
  • a representative map of the infrared absorption characteristics over the whole sample is built up by collecting FTIR spectra at room temperature with a 0.5 cm "1 resolution and an aperture size of 0.1-0.5 mm, the map containing a minimum of 10 data points.
  • One of the relationships above is then chosen based on the average measurement taken and used to derive the concentration of nitrogen for each position.
  • the uniformity is then judged from the frequency plot of the concentration measurements taken, assessing the percentage of measurements further away from the average than the limit to the deviation set.
  • SIMS analysis was typically performed using an O 2 + primary beam, with a primary voltage of 10 kV, a beam current of typically 1 ⁇ A and a spatial resolution of better than 50 ⁇ m.
  • Mapping was typically completed by stepping the analysis point on a 0.5 mm or 1 mm pitch over the face of the layer, obtaining from each face typically a minimum of 20 points and more preferably a minimum of 40 points.
  • Calibration was by comparison with implant standards.
  • Data from the SIMS was analysed by finding the mean of the dataset, and then finding the full range of the data expressed as a percentage of the mean for the different % fractions of the dataset, with the two opposite major faces of a layer given approximately equal weighting in order to characterise a volume. Reproducibility of the SIMS is typically of the order of 3-5%, dependent on conditions.
  • the material of this invention can be used in wide range of applications all of which have specific requirements on the geometry of the diamond used for their fabrication. It will thus be seen that controlling the morphology of the stone using the invention allows more efficient use of the synthesised material.
  • the applications described below are non-limiting and provided merely to demonstrate the required attributes of the material.
  • Single crystal cutting tool products are fabricated from a range of shapes and qualities of diamond depending on the application, market and cost requirement.
  • the most common shapes are rectangles for cutting applications and 'logs' for dressing grinding wheels. Other shapes are also used such as circles and triangles.
  • the majority of products have a four-point orientation for the largest planar face. This nomenclature refers to the sides of the products which are predominantly cut with edges parallel to a cubic or ⁇ 100> direction. Tools with two-point ⁇ 110> edges can also be made.
  • Dresser logs which are high aspect ratio rectangular prisms, for example have four-point all around and a four-point tip.
  • HPHT synthesis processes are developed to meet market requirements of cost, shape, quality and size. Some products are sold near net synthesis shape and some are highly engineered, high tolerance products. The challenge for HPHT synthesis is to maximise the usable volume of each crystal and stones from each synthesis run. Theoretically, the ideal way is to grow crystals without missing corners and truncated edges. Small crystals, of less than 4 mm edge length, should be grown near-net cubic shape requiring little removal from the large planar faces. There are two reasons for loss of volume. In the first case, the corners may be bound by octahedral ( ⁇ 111 ⁇ ) facets, as is seen in the central entry in the upper row of Table 1 and Figure 1.
  • the edges are curved and made less sharp by the presence of false facets, of the type shown in Fig 4.
  • more material has to be removed from both planar faces to open up the usable area of the crystal and reduce the truncation. Consequently, the usable volume yield from truncated crystals is considerably lower and the cost to process to usable shapes is higher.
  • the same principle applies to crystals with a larger edge length (typically greater than 4 mm). In this case, we would expect to be able to process the crystal to yield multiples of planar plates with larger areas. The extent to which this is possible depends upon the extent of the truncated corners and edges; therefore it is apparent that being able to control the morphology and reduce the impact is a significant advantage.
  • the teachings of this invention are central to the growth of a crystal showing an external morphology with a well defined shape, preferably a cubic shape, and well defined sharp edges. Whilst the nitrogen level is not the only factor contributing to the growth of crystals of the desired form, it is an important one. When using the teachings of this invention it becomes possible to control the amount of nitrogen added to the synthesis process in a systematic and reproducible way.
  • this invention enables greater than 10%, preferably greater than 20%, preferably greater than 30%, preferably greater than 40%, preferably greater than 50%, preferably greater than 60%, preferably greater than 70%, preferably greater than 80%, preferably greater than 90%, of the stones from a single run to have a CMI of less than 5.
  • this invention enables greater than 10%, preferably greater than 20%, preferably greater than 30%, preferably greater than 40%, preferably greater than 50%, preferably greater than 60%, preferably greater than 70%, preferably greater than 80%, preferably greater than 90%, of the stones from a single run to have a CMI of less than 4.
  • this invention enables greater than 10%, preferably greater than 20%, preferably greater than 30%, preferably greater than 40%, preferably greater than 50%, preferably greater than 60%, preferably greater than 70%, preferably greater than 80%, preferably greater than 90%, of the stones from a single run to have a CMI of less than 3.
  • this invention enables greater than 10%, preferably greater than 20%, preferably greater than 30%, preferably greater than 40%, preferably greater than 50%, preferably greater than 60%, preferably greater than 70%, preferably greater than 80%, preferably greater than 90%, of the stones from a single run to have a CMI of less than 2.
  • this invention enables greater than 10%, preferably greater than 20%, preferably greater than 30%, preferably greater than 40%, preferably greater than 50%, preferably greater than 60%, preferably greater than 70%, preferably greater than 80%, preferably greater than 90%, of the stones from a single run to have a CMI of greater than 5.
  • this invention enables greater than 10%, preferably greater than 20%, preferably greater than 30%, preferably greater than 40%, preferably greater than 50%, preferably greater than 60%, preferably greater than 70%, preferably greater than 80%, preferably greater than 90%, of the stones from a single run to have a CMI of greater than 6.
  • this invention enables greater than 10%, preferably greater than 20%, preferably greater than 30%, preferably greater than 40%, preferably greater than 50%, preferably greater than 60%, preferably greater than 70%, preferably greater than 80%, preferably greater than 90%, of the stones from a single run to have a CMI of greater than 7.
  • this invention enables the size distribution from any one synthesis run to be decreased compared with growing stones under the same conditions except for the nitrogen level.
  • This size distribution is expressed as a percentage of the average dimensions of the stones which have a maximum edge length (MEL) (as measured in the plane of the growth, i.e. perpendicular to the growth direction) as determined by measurements using digital callipers (or something similar) of the maximum dimensions.
  • MEL maximum edge length
  • the variation in the maximum edge length is such that greater than 25% of the as grown stones show a maximum variation expressed as a percentage of the average of less than 85%, preferably less than 70%, preferably less than 50%, preferably less than 40%, preferably less than 25%, preferably less than 15%, preferably less than 10%, preferably less than 5%.
  • the variation in the maximum edge length is such that greater than 40% of the as grown stones show a maximum variation expresses as a percentage of the average of less than 85%, preferably less than 70%, preferably less than 50%, preferably less than 40%, preferably less than 25%, preferably less than 15%, preferably less than 10%, preferably less than 5%.
  • the variation in the maximum edge length is such that greater than 60% of the as grown stones show a maximum variation expresses as a percentage of the average of less than 85%, preferably less than 70%, preferably less than 50%, preferably less than 40%, preferably less than 25%, preferably less than 15%, preferably less than 10%, preferably less than 5%.
  • the variation in the maximum edge length (MEL) is such that greater than 75% of the as grown stones show a maximum variation expresses as a percentage of the average of less than 85%, preferably less than 70%, preferably less than 50%, preferably less than 40%, preferably less than 25%, preferably less than 15%, preferably less than 10%, preferably less than 5%.
  • the variation in the maximum edge length is such that greater than 85% of the as grown stones show a maximum variation expresses as a percentage of the average of less than 85%, preferably less than 70%, preferably less than 50%, preferably less than 40%, preferably less than 25%, preferably less than 15%, preferably less than 10%, preferably less than 5%.
  • Nitrogen containing diamond material may be used in optically activated switches in which photons of energy less than the diamond band gap excite carriers from nitrogen-related defects to the valence or conduction bands.
  • the diamond it is beneficial for the diamond to be processed into plates contain a high and relatively uniform concentration of nitrogen. Since nitrogen concentration varies significantly between growth sectors, it is beneficial for such plates to be produced in such a way that they do not cross the boundaries between growth sectors.
  • the central ⁇ 100> sector formed above the seed crystal, has an area (measured perpendicular to the local growth direction) that increases as growth proceeds. When measured perpendicular to the local growth direction, the nitrogen concentration in the ⁇ 100> sectors is found to be uniform. This means that, by sawing perpendicular to the local growth direction, it is possible to process diamond plates of a range of different sizes from the central ⁇ 100> sector that have a nitrogen content that is both high and uniform.
  • the areas of such plates may range from approximately 1 mm x 1 mm to more than 5 mm x 5 mm.
  • the nitrogen concentration may be greater than 100 ppm, preferably greater than 150 ppm, preferably greater than 200 ppm, preferably greater than 250 ppm, preferably greater than 300 ppm, preferably greater than 350 ppm, preferably greater than 400 ppm, preferably greater than 450 ppm, preferably greater than 500 ppm, preferably greater than 550 ppm, preferably greater than 600 ppm, preferably greater than 650 ppm, preferably greater than 700 ppm, preferably greater than 750 ppm, preferably greater than 800 ppm, preferably greater than 900 ppm, preferably greater than 1000 ppm.
  • Diamond material is used as a material for sharp blades for applications such as eye surgery. For such sharp blades it is particularly important for the precise position of the cutting edge to be clearly seen by the user.
  • the high and uniform nitrogen content of the material of the current invention makes it uniformly dark even in relatively thin slices suitable for cutting blades. It is generally beneficial for such blades to have a longest dimension of at least 3 mm, preferably 4 mm, preferably 5 mm, preferably 6 mm, preferably 6.5 mm. Thin slices cut from the large diamond samples grown using the method of the current invention therefore have the required dimensions and optical properties for this application. It is further found that the near-cubic morphology (i.e. CMI of greater than 6) of the stones enables blades to be produced with a higher yield than from stones with lower CMI values.
  • CMI near-cubic morphology
  • Diamond is often used as a material for anvils for research involving generation of high pressures and temperatures. In such work it is desirable for the material under investigation to be thermally insulated so that high temperatures may be more easily generated and maintained. It is well known that the high thermal conductivity of diamond is reduced as the nitrogen content increases. It is therefore possible to modify and control the thermal conductivity of diamond by doping it with nitrogen, thereby producing designer diamond anvils suited to particular experiments. Diamond anvils are generally produced with a shape approximately the same as that of a round brilliant gemstone and when they are produced from HPHT synthesized material it may be beneficial for them to be produced from a single growth sector so that they have uniform thermal conductivity characteristics.
  • the method of the current invention can be used to produce large diamond crystals with a high and controlled nitrogen concentration (for a given growth sector) and in such a way that a large round brilliant anvil can be cut from the central ⁇ 100> sector that forms above the seed crystal.
  • a round brilliant anvil has a controlled and uniform thermal conductivity that is beneficial in experiments involving generation of high pressures and temperatures.
  • the uniform nitrogen is also critical to minimize and strain variation due to variations for example in lattice parameter which might limit the ultimate pressures the anvils can be used at in experimentation. Given the shape of a round brilliant and how it fits into an octahedron, it is clear that being able to synthesise stones of high CMI (i.e. octahedra) will be advantageous to the fabrication of such anvils. (See Figure 9.)
  • N concentration greater than 100 ppm, preferably greater than 200 ppm, preferably greater than 300 ppm, preferably greater than 400 ppm, preferably greater than 500 ppm, preferably greater than 1000 ppm.
  • the material will have a variation in N ( ⁇ N as defined above) of less than 100% over a volume greater than 1 mm 3 , preferably greater than 1.5 mm 3 , preferably greater than 3 mm 3 , preferably greater than 4 mm 3 , preferably greater than 5 mm 3 , preferably greater than 6 mm 3 , preferably greater than 7 mm 3 , preferably greater than 8 mm 3 , preferably greater than 10 mm 3 , preferably greater than 12 mm 3 , preferably greater than 15 mm 3 , preferably greater than 18 mm 3 , preferably greater than 20 mm 3 .
  • the material will have a variation in N (defined above) of less than 75% over a volume greater than 1 mm 3 , preferably greater than 1.5 mm 3 , preferably greater than 3 mm 3 , preferably greater than 4 mm 3 , preferably greater than 5 mm 3 , preferably greater than 6 mm 3 , preferably greater than 7 mm 3 , preferably greater than 8 mm 3 , preferably greater than 10 mm 3 , preferably greater than 12 mm 3 , preferably greater than 15 mm 3 , preferably greater than 18 mm 3 , preferably greater than 20 mm 3 .
  • the material will have a variation in N (defined above) of less than 50% over a volume greater than 1 mm 3 , preferably greater than 1.5 mm 3 , preferably greater than 3 mm 3 , preferably greater than 4 mm 3 , preferably greater than 5 mm 3 , preferably greater than 6 mm 3 , preferably greater than 7 mm 3 , preferably greater than 8 mm 3 , preferably greater than 10 mm 3 , preferably greater than 12 mm 3 , preferably greater than 15 mm 3 , preferably greater than 18 mm 3 , preferably greater than 20 mm 3 .
  • the material will have a variation in N (defined above) of less than 40% over a volume greater than 1 mm 3 , preferably greater than 1.5 mm 3 , preferably greater than 3 mm 3 , preferably greater than 4 mm 3 , preferably greater than 5 mm 3 , preferably greater than 6 mm 3 , preferably greater than 7 mm 3 , preferably greater than 8 mm 3 , preferably greater than 10 mm 3 , preferably greater than 12 mm 3 , preferably greater than 15 mm 3 , preferably greater than 18 mm 3 , preferably greater than 20 mm 3 .
  • the material will have a variation in N (defined above) of less than 30% over a volume greater than 1 mm 3 , preferably greater than 1.5 mm 3 , preferably greater than 3 mm 3 , preferably greater than 4 mm 3 , preferably greater than 5 mm 3 , preferably greater than 6 mm 3 , preferably greater than 7 mm 3 , preferably greater than 8 mm 3 , preferably greater than 10 mm 3 , preferably greater than 12 mm 3 , preferably greater than 15 mm 3 , preferably greater than 18 mm 3 , preferably greater than 20 mm 3 .
  • the material will have a variation in N (defined above) of less than 20% over a volume greater than 1 mm 3 , preferably greater than 1.5 mm 3 , preferably greater than 3 mm 3 , preferably greater than 4 mm 3 , preferably greater than 5 mm 3 , preferably greater than 6 mm 3 , preferably greater than 7 mm 3 , preferably greater than 8 mm 3 , preferably greater than 10 mm 3 , preferably greater than 12 mm 3 , preferably greater than 15 mm 3 , preferably greater than 18 mm 3 , preferably greater than 20 mm 3 .
  • the material of the current invention may also find applications as a gemstone in jewellery. If the material is used in its as-grown form, such gemstones will have a dark colour which may be considered desirable according to personal preferences and fashions. Alternatively the colour of the material may be altered by one or more post-growth treatments. Gemstones produced from material produced by the method of the current invention may either comprise more than one growth sector but when uniformity of colour is desired it is considered that it is beneficial for their majority volume to comprise a single growth sector. This is particularly the case when the colour has been lightened by post-growth treatment. Using the method of the current invention, a large and uniformly coloured round brilliant can be produced from the central ⁇ 100> sector that is formed above the seed crystal.
  • the low metal content of the stones of this invention is beneficial to the appearance of the stone.
  • the cutting of gemstones from high CMI stones may be geometrically more efficient that cutting them from low CMI stones (i.e. cubes).
  • the size should be greater than 3 mm x 3 mm, preferably greater than 3.5 mm x 3.5 mm, preferably greater than 4 mm x 4 mm, preferably greater than 4.5 mm x 4.5 mm, preferably greater than 5 mm x 5 mm, preferably greater than 5.5 mm x 5.5 mm, preferably greater than 6 mm x 6 mm, preferably greater than 8 mm x 8 mm, preferably greater than 10 mm x 10 mm, preferably greater than 15 mm x 15 mm.
  • material of this invention offers:
  • the change in nitrogen (defined above), ⁇ N over an area of 2 mm x 2 mm of less than 90%, preferably ⁇ N over an area of 2 mm x 2 mm of less than 80%, preferably ⁇ N over an area of 2 mm x 2 mm of less than 70%, preferably ⁇ N over an area of 2 mm x 2 mm of less than 60%, preferably ⁇ N over an area of 2 mm x 2 mm of less than 50%; preferably ⁇ N over an area of 2 mm x 2 mm of less than 40%.
  • ⁇ N over an area of 3 mm x 3 mm of less than 90% preferably ⁇ N over an area o3 mm x 3 mm of less than 80%, preferably ⁇ N over an area of 3 mm x 3 mm of less than 70%, preferably ⁇ N over an area of 3 mm x 3 mm of less than 60%, preferably ⁇ N over an area of 3 mm x 3 mm of less than 50%; preferably ⁇ N over an area of 3 mm x 3 mm of less than 40%.
  • ⁇ N over an area of 3.5 mm x 3.5 mm of less than 90% preferably ⁇ N over an area of 3.5 mm x 3.5 mm of less than 80%, preferably ⁇ N over an area of 3.5 mm x 3.5 mm of less than 70%, preferably ⁇ N over an area of 3.5 mm x 3.5 mm of less than 60%, preferably ⁇ N over an area of 3.5 mm x 3.5 mm of less than 50%; preferably ⁇ N over an area of 3.5 mm x 3.5 mm of less than 40%.
  • ⁇ N over an area of 4 mm x 4 mm of less than 90% preferably ⁇ N over an area of 4 mm x 4 mm of less than 80%, preferably ⁇ N over an area of 4 mm x 4 mm of less than 70%, preferably ⁇ N over an area of 4 mm x 4 mm of less than 60%, preferably ⁇ N over an area of 4 mm x 4 mm of less than 50%; preferably ⁇ N over an area of 4 mm x 4 mm of less than 40%.
  • ⁇ N over an area of 4.5 mm x 4.5 mm of less than 90% preferably ⁇ N over an area of 4.5 mm x 4.5 mm of less than 80%, preferably ⁇ N over an area of 4.5 mm x 4.5 mm of less than 70%, preferably ⁇ N over an area of 4.5 mm x 4.5 mm of less than 60%, preferably ⁇ N over an area of 4.5 mm x 4.5 mm of less than 50%; preferably ⁇ N over an area of 4.5 mm x 4.5 mm of less than 40%.
  • ⁇ N over an area of 5 mm x 5 mm of less than 90% preferably ⁇ N over an area of 5 mm x 5 mm of less than 80%, preferably ⁇ N over an area of 5 mm x 5 mm of less than 70%, preferably ⁇ N over an area of 5 mm x 5 mm of less than 60%, preferably ⁇ N over an area of 5 mm x 5 mm of less than 50%; preferably ⁇ N over an area of 5 mm x 5 mm of less than 40%.
  • ⁇ N over an area of 6 mm x 6 mm of less than 90% preferably ⁇ N over an area of 6 mm x 6 mm of less than 80%, preferably ⁇ N over an area of 6 mm x 6 mm of less than 70%, preferably ⁇ N over an area of 6 mm x 6 mm of less than 60%, preferably ⁇ N over an area of 6 mm x 6 mm of less than 50%; preferably ⁇ N over an area of 6 mm x 6 mm of less than 40%.
  • the inventors believe that the properties of the material of the invention, in particular the low and uniform strain and the ability to cut large single sector plates without missing corners from the crystals could make this material suitable for use as an x- ray optical material in synchrotrons and other demanding areas.
  • Figure 1 Definition of the crystal morphology index for crystals grown uniformly in three dimensions.
  • Figure 2 When growing from a seed up into a half-space, only the top half of the circumscribing cube is apparent, but the same construction can be applied to the view in plan from above. Here is a cmi 3 crystal but seen here at a low angle to illustrate the effect.
  • Figure 3 Plan view from above (seed at bottom). Entries in the table match the entries in Table 1.
  • Figure 4 At intermediate levels of nitrogen, 50 to 100 ppm, there is rounding and curvature of crystal faces, leading to a loss of useful mass.
  • FIG. 5 Diamonds grown using the teachings of this invention showing higher nitrogen content (darker colour) and better shape
  • Figure 6 Diamonds grown using the prior art and showing a lower nitrogen level, (lighter colour) and less useful shape, with more rounding and minor faces.
  • Figure 7 The beneficial action of nitrogen is illustrated. As the nitrogen concentration in the cubic sector (central goblet shaped region) is decreasing, the relative sizes of the cubic and octahedral sectors changes in the direction of a more octahedral, high CMI crystal.
  • Figure 8 Showing material of the invention grown at high temperature.
  • Figure 9 Showing how a RBC gem (anvil) can be cut from a single growth sector from a low CMI stone.
  • a sample of two kilograms of cobalt powder of purity 99% and containing 25 ppm of nitrogen as received from the supplier was treated in a commercial nitriding furnace at 750 0 C in a stream of dry ammonia at one to two inches of water gauge positive pressure for 10 hours. After this time the nitrogen level was measured again by the same method and found to have increased to 592 ppm.
  • a component of 11.2% by weight percentage of this powder was added to the cobalt-iron solvent metal catalysts used in this diamond synthesis process.
  • the synthesis process was carried out at typical conditions of temperature, 125O 0 C to 1300 0 C and 5 to 6 GPa.
  • a representative sub-sample of the diamonds grown in this process is shown in Figure 5. These were characterized by FTIR.
  • the average nitrogen concentration within the central ⁇ 100 ⁇ sector was 630 ppm, throughout the whole stone it was 490 ppm.
  • the average CMI of the stones produced in this synthesis run was 2.8.
  • Example 1 was repeated with the exception the synthesis temperature was increased by 100 0 C, this produced the material shown in Figure 8.
  • the average nitrogen concentration of the most octahedral stones was 652 ppm.
  • the average CMI was 6.5.

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Abstract

La présente invention concerne un matériau à base de diamant synthétique ayant au moins deux des caractéristiques suivantes : (i) une teneur en azote égale ou supérieure à 100 ppm ; (ii) un indice de morphologie cristalline (CMI) soit inférieur à quatre (4) soit supérieur à six (6) ; (iii) une distribution uniforme d'azote dans le volume majoritaire du cristal, le volume majoritaire étant égal ou supérieur à 50% du volume total du cristal ; (iv) une faible teneur en impureté de métal de transition, 'faible' représentant moins de 100 ppm en poids ; et (v) une forme cristalline exempte de facettes mineures, 'facettes mineures' signifiant toutes les facettes autres que des facettes {100} et {111}. L'invention concerne également un procédé de production de matériau à base de diamant comprenant l'étape de mise à disposition d'une masse réactionnelle comportant suffisamment d'azote pour permettre d'obtenir un matériau à base de diamant ayant une teneur en azote égale ou supérieure à 100 ppm en combinaison avec un vecteur de métal de transition et le traitement de la masse réactionnelle à une température supérieure à 1200°C et une pression supérieure à 5 GPa.
PCT/IB2007/052751 2006-07-10 2007-07-10 Procédé de production de matériau à base de diamant Ceased WO2008007336A2 (fr)

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Cited By (6)

* Cited by examiner, † Cited by third party
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WO2015135979A1 (fr) * 2014-03-14 2015-09-17 Element Six (Uk) Limited Grains de diamant, outils les comprenant et leurs procédés d'utilisation
WO2016203950A1 (fr) * 2015-06-19 2016-12-22 住友電気工業株式会社 Monocristal de diamant, outil et procédé de fabrication de monocristal de diamant
WO2017198662A1 (fr) * 2016-05-17 2017-11-23 Element Six (Uk) Limited Pièce d'outil en diamant
CN115232615A (zh) * 2022-06-23 2022-10-25 西安电子科技大学 硅空位色心发光强度可调控的微晶金刚石晶粒的制备方法
US20220389300A1 (en) * 2019-10-24 2022-12-08 Sekisui Chemical Co., Ltd. Resin composition and heat-dissipating member
CN118996598A (zh) * 2024-08-19 2024-11-22 河南省科研平台服务中心 一种钴触媒高氮大尺寸单晶金刚石生长的方法

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NL128759C (fr) * 1965-11-13
US4174380A (en) * 1976-07-21 1979-11-13 General Electric Company Annealing synthetic diamond type Ib
IL81537A (en) * 1986-02-24 1991-05-12 De Beers Ind Diamond Method and synthetic diamond detector for detection of nuclear radiation
JPH0288498A (ja) * 1988-06-13 1990-03-28 Sumitomo Electric Ind Ltd ダイヤモンドレーザ結晶およびその作製方法
US6887144B2 (en) * 1996-11-12 2005-05-03 Diamond Innovations, Inc. Surface impurity-enriched diamond and method of making
US7404857B2 (en) * 1997-04-04 2008-07-29 Chien-Min Sung Superabrasive particle synthesis with controlled placement of crystalline seeds

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2015135979A1 (fr) * 2014-03-14 2015-09-17 Element Six (Uk) Limited Grains de diamant, outils les comprenant et leurs procédés d'utilisation
WO2016203950A1 (fr) * 2015-06-19 2016-12-22 住友電気工業株式会社 Monocristal de diamant, outil et procédé de fabrication de monocristal de diamant
JP2017007887A (ja) * 2015-06-19 2017-01-12 住友電気工業株式会社 ダイヤモンド単結晶、工具およびダイヤモンド単結晶の製造方法
WO2017198662A1 (fr) * 2016-05-17 2017-11-23 Element Six (Uk) Limited Pièce d'outil en diamant
US11253925B2 (en) 2016-05-17 2022-02-22 Element Six (Uk) Limited Diamond tool piece
US20220389300A1 (en) * 2019-10-24 2022-12-08 Sekisui Chemical Co., Ltd. Resin composition and heat-dissipating member
CN115232615A (zh) * 2022-06-23 2022-10-25 西安电子科技大学 硅空位色心发光强度可调控的微晶金刚石晶粒的制备方法
CN115232615B (zh) * 2022-06-23 2024-01-23 西安电子科技大学 硅空位色心发光强度可调控的微晶金刚石晶粒的制备方法
CN118996598A (zh) * 2024-08-19 2024-11-22 河南省科研平台服务中心 一种钴触媒高氮大尺寸单晶金刚石生长的方法

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